This section provides background information related to the present disclosure which is not necessarily prior art. This section also provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
Gas chromatographic microsystems (μGCs) offer the potential for analyzing mixtures of volatile organic compounds (VOCs) in miniature packages suitable for personal exposure monitoring, point-of-care medical diagnostics, explosive detection, and other applications. Typical μGCs may include an accumulator, a sample injector, a separation column, and a detector, each of which may be fabricated from Si, glass, or other suitable materials, and are generally provided as separate devices or components.
It may be necessary, however, to concentrate the VOC(s) of interest prior to analysis because detectors may lack the inherent sensitivity required to attain the low detection limits demanded in many applications. For this reason, μGC injectors may incorporate a preconcentration function and may include a device with an internal cavity packed or lined with an adsorbent material. The VOCs in an air sample, drawn through the device by means of a small pump, are trapped on the surface of a generally high-surface-area solid adsorbent. Subsequent rapid heating leads to desorption into a carrier gas flowing at a lower rate, which leads to an enhancement in concentration of the VOCs that are passed downstream to a measurement device such as a separation microcolumn and/or a microsensor or microsensor array.
One factor that may affect performance is the dynamic adsorption capacity, which is related to the volatility and functionality of the VOC(s), the mass and specific surface area of the adsorbent (and therefore the size/mass of the device), and the flow rate of the air sample being drawn through the device. Other performance factors may include the desorption rate, efficiency, and bandwidth, which are also related to the volatility and functionality of the VOC(s), the mass and surface area of the adsorbent, and the desorption/injection flow rate, as well as the maximum temperature and rate at which the device is heated. Power requirements may also be a concern, and often have a significant influence on device design.
As progress is made toward smaller and more power efficient components, the power required for pumping becomes more significant. For example, most μGC systems rely on commercial mini-pumps, which dissipate on the order of 1 W-4 W. Depending on the required sample volume and the time of analysis, the energy for pumping may exceed that for the other power-intensive components.
It is desirable for VOC samplers to be small (i.e., a few cubic centimeters), employ carbon based trapping materials, and have sampling rates of about 3 to 30 mL/min. With known devices, following the sample collection period, typically 4-24 hours of using a pump device to collect the sample, the device is returned to the laboratory for solvent or thermal desorption followed by conventional measurement analysis. There remains a need for even smaller samplers, and samplers that are more convenient to use with little or no energy consumption during collection.
The present technology provides a passive preconcentrator and injector device. The device may include an upper portion defining an array of micro-scale diffusion channels, and a lower portion defining a cavity in fluid communication with the micro-scale diffusion channels. A collection material may be disposed within the cavity and configured to capture at least one gas-phase analyte. An integral heating unit may be disposed in thermal communication with the lower portion and configured to heat the cavity. An inlet port and an outlet port may be provided in fluid communication with the cavity. The device may be configured to collect at least one compound in a gas phase at a known rate by using passive diffusion, without the use of artificial circulation, and subsequently remove the compound for injection to a measuring device.
According to various aspects of the present technology, the passive preconcentrator and injector device may include an upper plate defining an array of micro-scale diffusion channels, and a lower plate secured to the upper plate and defining a cavity in fluid communication with the micro-scale diffusion channels. An integral heating unit may be disposed on an exterior region of the lower plate and configured for heating the cavity. A loading port may be provided for introducing a reusable collection material, and an inlet port and an outlet port may be provided, both in fluid communication with the cavity. A fluidic manifold system comprising a plurality of conduits may be disposed between the cavity and the outlet port.
The present technology also provides a method of detecting a compound in the gas phase using a combination preconcentrator and injector device. The method comprises providing a passive preconcentrator and injector device including an upper portion defining an array of micro-scale diffusion channels, a lower portion defining a cavity in fluid communication with the micro-scale diffusion channels and containing a collection material, an integral heating unit, an inlet, and an outlet. The preconcentrator and injector device is exposed to a sampling area and the method allows for the collection material to passively capture a gas-phase analyte sample for a predetermined time period at a predetermined rate. The method includes connecting the outlet to a measurement device and actuating the integral heating unit and initiating thermal desorption to generate a desorbed gas or vapor. A desorbed gas or vapor is collected and analyzed to detect at least one captured or desorbed compound.
Further areas of applicability will become apparent from the drawings and description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.